1. Field of the Invention
The present invention relates generally to automobiles and other vehicles, and, more particularly, to an electrostatic occupant detection system.
2. Description of the Related Art
JP-A-11-271463 discloses an electrostatic occupant detection system that includes a mat-shaped electrostatic sensor and an occupant detection electronic control unit (ECU). The electrostatic sensor is supplied with a sine wave from the occupant detection ECU and generates an electric field between a main electrode disposed in a vehicle seat and a vehicle body. The electrostatic sensor outputs an electrical current or a voltage to the occupant detection ECU in accordance with a change in the electric field, and the occupant detection ECU determines the presence of an occupant based on the electrical current or the voltage. When the electrostatic occupant detection system performs a self diagnosis, in general, the occupant detection ECU stops supplying the sine wave to the electrostatic sensor and switches to a predetermined direct current (DC) voltage or the ground level only at an initial check during vehicle start-up.
The above-described occupant detection ECU supplies only the sine wave to the electrostatic sensor during the normal operation. It is preferred to correct variation in a detected capacitance of the electrostatic sensor based on the diagnosis of the electrostatic occupant detection system and a change in an environmental temperature even during the normal operation. In such a case, the sine wave supplied to the electrostatic sensor is stopped once and is switched to the predetermined DC voltage or the ground level. If the sine wave is rapidly switched to the DC voltage or the ground level, noise may be generated, the noise may adversely affect other electronic devices including a radio, and radio noise may be output.